Bad Admin Habits
Things to not do in your Salesforce Org - Do what I say, not what I do.
Not setting up Mini Page Layouts - they are so useful.
Not having Help Text on EVERY single custom field. Also include a description for WHY it was added.
Adding formula fields to child object so show data from the parent object - just add it to the mini page layout or Custom Report Types instead.
Heaps of checkboxes - Unless they are used for frequency reporting in place of a Multi Select Picklist. I HATE checkboxes because they can't be an explicit NO.
Not turning on Enhanced Profile View
Not investing in a tool like Rollup Helper or using Declarative Lookup Rollup Summary. There is so much that can be done with these tools.
Not installing apps like Kugamon Account Contact Sync
Not installing or setting up any form of dupe blocking.
Setting up reports to be exported - Question why you exporting data. Use Excel Power Query at least (unless over 2000 rows).
Export your data and back it up.
Not clearly identifying your test data so you can exclude it from reports.
Creating custom objects when a Standard object can be used.
Not linking with external apps - eg Mailchimp or Campaign Monitor
Not using Do Not Call and Do Not Email fields
Adding values into picklists that are used for only a short time
Not setting up page layouts to be logical order of fields and groupings.
Keeping related lists on page layouts that are not used.
Not removing Yahoo Maps custom links on Page Layouts - come on - you KNOW you will never click it - especially now with the new integrated maps
Not setting up Record Types.
Not setting up a custom App with only the tabs you need.
Adding system only or reporting only fields to page layouts - just use Salesforce Inspector Browser Extensions
Using Activities instead of the Feed.
Not using the Feed.
Adding Status fields on the object.
Worse still, adding Latest contact fields on the object. USE THE FEED!
Adding ALL the information into the Description field.
Having a text field rather than a picklist when reporting on that field and expecting consistent values.
Reporting on Tasks - WHY - who ever looks at these reports? Do you not trust your staff?
Using Tasks to remind people to do stuff. See Action Views, Tasks and Report Alerts
Having Excel spreadsheets that relate to any data in Salesforce
Doing an import into multiple objects on a regular basis and not using something like Skyvva or one of the Excel based tools to do it quickly and easily.
Having ANY fields in your org that you don't know what they do.
Having ANY records in Salesforce that you can't immediately say why they exist and what benefit they have to the business.
Importing data and not including a Data Source - where did this data come from?
Using the Account or Contact record as the place to update information about other records - eg the status of outstanding payments - unless of course it is automated by a Rollup.
Entering Names in a text field - eg the Accounts Payable name - NOPE. Add a Contact with a Type of Accounts Payable, and add that as a lookup to the Account.
Ammending the ALL views to have filter criteria on them so they don't actually return ALL records.
Reports
Not hiding unused report types
Not deleting sample reports